MEMS millimeter wave switches

ABSTRACT

An RF switch useable up to millimeter wave frequencies and higher frequencies of 30 GHz and above. Four embodiments of the invention are configured as ground switches. Two of the ground switch embodiments are configured with a planar air bridge. Both of these embodiments are configured so that the bridge length is shortened between the transmission line and ground by introducing grounded stops. The other two ground switch embodiments include an elevated metal seesaw. In these embodiments, a shortened path to ground is provided with relatively low inductance by proper sizing and positioning of the seesaw structure. Lastly, broadband power switch embodiment is configured to utilize only a small portion of the air bridge to carry the signal. The relatively short path length results in a relatively low inductance and resistance lowers the RF power loss of the switch, thereby increasing the RF power handling capability of the switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a reissue continuation application of co-pendingU.S. patent Reissue application Ser. No. 11/334,823, filed on Jan. 17,2006, which is a re-issue of U.S. patent application Ser. No.10/320,926, filed on Dec. 16, 2002, which issued as U.S. Pat. No.6,873,223 on Mar. 29, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to millimeter wave switches and moreparticularly to millimeter wave switches useful at millimeter wavefrequencies and higher frequencies with increased power handlingcapability relative to known switches, amenable to being fabricatedusing microelectromechanical system (MEMS) technology.

2. Description of the Prior Art

RF switches are used in a wide variety of applications. For example,such RF switches are known to be used in variable RF phase shifters, RFsignal switching arrays, switchable tuning elements, as well as bandswitching of voltage controlled oscillators. In order to reduce the sizeand weight of such RF switches, microelectromechanical system (MEMS)technology has been known to be used to fabricate such switches. Anexample of such an RF switch is disclosed in commonly owned U.S. Pat.No. 6,218,911, hereby incorporated by reference. The RF switch disclosedtherein includes a pair of relatively parallel spaced apart metaltraces. An air-bridged metal beam is disposed between the parallelspaced apart metal traces.

Electrostatic forces are used to deflect the air bridge to contact oneof the metal traces. The center beam is attached to a substrate at eachend. As such, when electrostatic attraction forces are applied, the beamdeflects into a U-shaped configuration, such that a point approximatelyat the center of the beam, contacts one of the parallel metal tracesdisposed adjacent the beam. In such a configuration, the RF input isapplied to one end of the beam.

Although such a configuration provides satisfactory performance, such aconfiguration has a relatively high impedance (i.e. relatively highinductive and resistance) which results in relatively high RF powerlosses, and reduces the RF power capability of the switch.

In order to solve the problem of high RF power losses of such switches,capacitive-type switches using MEMS technology have been developed foruse in millimeter wave and microwave applications. Such capacitive-typeswitches include a lower electrode, a dielectric layer and a movablemetal membrane. Electrostatic forces are used to cause the movable metalmembrane to snap and make contact with the dielectric layer to form acapacitive-type switch. Examples of these capacitive-type switches aredisclosed in: “Performance of Low Loss RF MEMS Capacitive Switches,” byGoldsmith et al., IEEE Microwave and Guided Wave Letters, Vol. 8, No. 8,August 1998, pgs. 269, 271; and “Ka-Band RF MEMS Phase Shifters,” byPillans et al., IEEE Microwave and Guided Wave Letters, Vol. 9, No. 12,December 1999, pgs 520-522. Although such capacitive-type switchesprovide adequate performance in the millimeter wave and microwavefrequencies, the dielectric layer in the capacitive-type switches isknown to store charges making it unsuitable for commercial applications.Thus, there is a need for an RF switch which provides truemetal-to-metal contact which avoids problems associated withcapacitive-type switching and also provides increased RF power handlingcapability relative to known RF switches.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention relates to various embodiments of an RFswitch suitable for use at millimeter wave and higher frequencies of 30GHz and above. All embodiments of the switch are configured to reduceportions of the switch structure which are not 50 ohm transmission linesin order to reduce the RF power losses of the switch and increase its RFpower handling capability. Four embodiments of the invention areconfigured as ground switches. Two of the ground switch embodiments areconfigured with a planar air bridge. Both of these embodiments areconfigured so that the conduction path length in the air bridge isshortened between the transmission line and ground by introducinggrounded stops. The other two ground switch embodiments include anelevated metal seesaw. In these embodiments, a shortened path to groundis provided with relatively low inductance by proper sizing andpositioning of the seesaw structure. Lastly, a broadband power switchembodiment is configured to utilize only a small portion of the airbridge to carry the signal. The relatively short path length results ina relatively low inductance and resistance which reduces the RF powerlosses of the switch and increases its RF power handling capabilityrelative to known RF switches.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention will be readilyunderstood with reference to the following specification and attacheddrawings wherein:

FIG. 1 is a plan view of a ground switch formed with a planar airbridge.

FIG. 2 is a plan view of alternate embodiment of the ground switch witha planar air bridge illustrated in FIG. 1.

FIG. 3A is a plan view of another embodiment formed as a ground switchwith an elevated metal seesaw mounted between two fixed posts by way oftorsion bars.

FIG. 3B is an elevational view of the embodiment illustrated in FIG. 3A,shown in a clockwise position.

FIG. 3C is similar to FIG. 3B, but shown in a counterclockwise position.

FIG. 4 is a plan view of an alternate embodiment of the ground switchillustrated in FIG. 3.

FIG. 5 is a plan view of single pole double throw broadband power switchin accordance with an alternate embodiment of the invention with atransverse air bridge shown with no control bias applied.

FIG. 6 is similar to FIG. 5 but shown with a bias applied to the rightcontrol electrodes.

FIG. 7 is similar to FIG. 5 but shown with a bias applied to the leftcontrol electrodes.

FIG. 8 is similar to FIG. 5 but configured with two air bridges.

FIGS. 9A-9J are exemplary process flow diagrams for fabricating the airbridge and seesaw type switches illustrated in FIG. 1-4.

FIGS. 10A-10C are diagrams identifying the various metal layers for theseesaw type switches illustrated in FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, various embodiments ofmillimeter wave switches are illustrated in FIGS. 1-8. In particular,FIGS. 1 and 2 illustrate ground switches which incorporate a planar airbridge. FIGS. 3A and 4 illustrate alternate embodiments of a groundswitch formed with an elevated seesaw connected between two fixed postsby way of torsion bars. FIGS. 5-7 illustrate an embodiment of abroadband power switch, shown, for example, as a single pole doublethrow switch. Finally, FIG. 8 illustrates an embodiment of the broadbandpower switch, illustrated in FIG. 7, but formed with a pair oftransverse air bridges.

In all embodiments, the path lengths between the transmission line andground are shortened relative to known RF switches. By shortening thesepath lengths, the inductance and resistance of the structure is therebylowered, thereby lowering the RF power losses of the switch andincreasing its power handling capability.

Two embodiments of a grounding switch formed with a planar air bridgeillustrated in FIGS. 1 and 2 are useful as an RF switch at millimeterwave frequencies and higher frequencies of 30 GHz and above. Both ofthese embodiments may be fabricated utilizing microelectro-mechanicalswitch (MEMS) technology, for example, as disclosed in commonly-ownedU.S. Pat. No. 6,218,911, hereby incorporated by reference. FIG. 1 is anembodiment with a transverse air bridge, while FIG. 2 is configured witha parallel air bridge. As will be discussed in more detail below, bothembodiments utilize grounded stops which shorten the conduction pathlength in the bridge between the transmission line and ground, therebyreducing the impedance and RF power loss of the switch.

Referring first to FIG. 1, a first embodiment of the millimeter wavegrounding switch is illustrated and generally identified with thereference numeral 20. The grounding switch 20 includes an air bridgedbeam 22, for example, 2 micrometers wide, 2 micrometers thick and 300micrometers long, formed between two end posts 24 and 26, which, inturn, are attached to a substrate (not shown). The end posts 24 and 26are, in turn, connected to ground. A microstrip transmission line 25,carried by the substrate (not shown), is formed transverse to the airbridge beam 22. In this embodiment, an RF input is applied to one end ofthe microstrip transmission line 25, while an RF output is available atan opposing end of the microstrip transmission line 25. In operation,during a condition when there is no deflection or actuation of themillimeter wave switch 20, as shown, the RF input applied to themicrostrip transmission line 25 passes through unaffected. However, aswill be discussed in more detail below, actuation of the millimeter waveswitch 20 causes the microstrip transmission line 25 to be effectivelygrounded, thereby reflecting 100% of the RF input, thereby emulating anopen switch.

A fixed RF contact 27 is formed, for example, on the microstriptransmission line 25 or a co-planar RF transmission line with animpedance of about 50 ohms (not shown). The contact 27 connects the beam22 to the microstrip transmission line 25 in an actuated position. Inaccordance with an important aspect of the invention, one or more groundstops 28, 30, formed, for example, adjacent the microstrip transmissionline 25 as shown, effectively reduce the path length of the air bridge22, thereby reducing the impedance and RF power losses of the switch 20.As shown the ground stops 28, 30 are formed on the same side of the airbridge 22 as the fixed RF contact 27.

By appropriate placement of the ground stops 28, 30, the effective pathlength can be made to be about 50 micrometers or less. A relativelyshort path length provides a relatively good RF ground for themicrostrip transmission line 25 up to millimeter wave frequencies. Assuch, the RF ground makes an effective RF reflection in the microstriptransmission line 25 when the beam 22 is attracted thereto allowingeffective switching in circuits, such as a Ka-band phase shifter. Incontrast, the path length of the RF switch disclosed in commonly ownedU.S. Pat. No. 6,218,911 is approximately half the length of the airbridge or about 150 micrometers.

Two control pads 32 and 34 are provided. These control pads 32, 34 areused to cause deflection of the beam 22 by electrostatic forces. Assuch, when a bias voltage, for example, +50V, is applied to each of thecontrol pads 32, 34, the beam 22 is deflected by electrostatic force soas to be electrically connected to the fixed RF contact 27 and fixedgrounded stops 28, 30, effectively producing a relatively short pathfrom the microstrip 25 transmission line to ground.

The reliability of the ground switch 20 may be increased by adding oneor more optional control pads 36, 38 to the left side (FIG. 1) of thebeam 22 and one or more additional ground stops 40, 42. The additionalcontrol pads 36, 38 and ground stops 40, 42 allow the beam 22 to breakaway from the actuated position by force in case it sticks.Additionally, the additional control pads 36, 38 and ground stops 40, 42allow for symmetrical switch movement in both directions with the sameamount of bending in each direction which tends to prevent any permanentbending from occurring in the beam 22. Alternatively, the stops 40, 42may be configured as electrically “floating” so that the switch isgrounding when the bridge is pulled to the right, and non-grounding whenthe bridge is pulled to the left.

An alternative embodiment of the ground switch 20 is illustrated in FIG.2. Referring to FIG. 2, the ground switch, generally identified with thereference numeral 44, is disposed generally in parallel and adjacent tothe microstrip transmission line 46, formed on a substrate, not shown.The ground switch 44 operates in a similar manner as the ground switch20.

An air bridge beam 48 is formed on the substrate (not shown) andconnected thereto by way of two end posts 50 and 52, formed, forexample, by a 2 micrometer metal deposition on the substrate. In thisembodiment, the air bridge beam 48 is parallel to the microstriptransmission line 46. An RF Input is available on one end of themicrostrip 46 and an RF Output is available on the other end. A terminal54 is formed between the microstrip transmission line 46 and the beam48. A grounded stop 56 is positioned adjacent the beam 48 on a sideopposite the terminal 54. A control pad 58 is disposed adjacent the beam48 on the same side as the grounded stop 56.

When a biasing voltage, either positive, for example +50V, or a negativevoltage, is applied to the control pad 58, the left side of the beam(i.e. portion of the beam left of the grounded stop 56 as viewed in FIG.2) is attracted to the control pad 58. Because of the rigidity of thebeam, the beam 48 is twisted so that a right portion is deflected towardthe microstrip transmission line 46 and contacts the terminal 54 on themicrostrip transmission line 46 as well as the grounded stop 56. In thisposition, the microstrip transmission line 46 is connected to groundwith a length of only about 25% of the total air bridge length. Byreducing the path length to about 25%, the millimeter wave switch 44 hasreduced RF power loss and increased power handling capability.

FIGS. 3A and 4 illustrate ground switches configured as seesaws inaccordance with alternate embodiments of the invention which provide arelatively short path to ground, thereby resulting in a relatively lowinductance. The short path length in the case of the seesaw-typeswitches is made possible by proper sizing and positioning of the seesawstructure. In particular, the relatively wide dimensions of the seesawresult in a relative low inductance. As such, by reducing theinductance, the millimeter wave switch 60 will have lower RF powerlosses. In the embodiment illustrated in FIG. 3 3A, a seesaw structurestraddles a transmission line and connects it to grounds on both ends.In the embodiment illustrated in FIG. 4, the seesaw is disposed adjacentone edge of a transmission line and grounds the one edge.

Referring to FIG. FIGS. 3A-3C, a first embodiment of the seesawgrounding switch, generally identified with the reference numeral 60(FIG. 3a), is illustrated. In this embodiment, an elevated metal seesaw62 is provided. The seesaw 62 is located above a microstrip transmissionline 64 (FIG. 3a) that is mounted, in turn, to a substrate (not shown).An RF Input is available on one end of the microstrip 64 and an RFOutput is available on the other end. The seesaw 62 is mounted to twofixed posts 65, 66, connected to the substrate by way of a pair oftorsion bars 68 and 70, as shown in FIG. 3a. The end posts 65 and 66 aregrounded. Thus, when the seesaw 62 rotates clockwise orcounter-clockwise about an axis through the end posts 65, 66, generallyperpendicular to a longitudinal axis of the transmission line 64, themicrostrip 64 is grounded by way of the seesaw 62.

Various control pads 72 (FIGS. 3a, 3b), 74 (FIGS. 3a, 3c), 76 (FIGS. 3a,3c), and 78 (FIGS. 3a, 3b) may be provided. These control pads 72-78 aredisposed on the substrate beneath the seesaw 62. When a bias voltage,for example 10 V, is applied to the control pads (as shown in FIG. 3a),electrostatic attraction forces cause the seesaw 62 to rotate. Moreparticularly, when a bias voltage is applied to the control pads 72 and76, the seesaw 62 will rotate in a clockwise direction. Similarly, whena bias voltage is applied to the control pad 74 and 78, the seesaw 62rotates in a counterclockwise direction. As will be discussed in detailbelow, the seesaw 62 does not contact any of the control pads 72-78 72,74, 76 and 78 in a full clockwise or counter-clockwise position.

Such an arrangement provides a mechanical push-pull configuration.Accordingly, if the switch 60 sticks in one position, it can be returnedto a normal position by removing the biasing voltage from the controlpads in the stuck position and applying a biasing voltage to theopposite control pads. For example, if the switch is stuck in a positionwhereby the seesaw 62 is stuck in a clockwise position, the biasingvoltage is removed from the control pads 72 and 76 and applied to thecontrol pads 74 and 78. Application of the biasing voltage to thecontrol pad 74 and 78, in turn, causes the seesaw 62 to rotate in acounterclockwise direction, thus returning the seesaw 62 to an at restposition.

Like the grounding switches illustrated in FIGS. 1 and 2, the switch 60also causes a grounding of the RF input signal and thus may be used as aground switch for the microstrip transmission line 64. A terminal may beformed on the microstrip 64 beneath the seesaw 62. The terminal (notshown) may be used as a contact point.

In order to prevent the seesaw 62 from contacting the control pads 72,76 when the millimeter wave switch 60 is actuated in the clockwisedirection, optional electrically “floating” stops 80, 82 may be providedon the substrate, under the right end of the seesaw 62. These stops 80,82 may be used to prevent the seesaw 62 from contacting the microstriptransmission line 64 when the switch is in the clockwise non-groundingposition as shown in FIG. 3B. When a bias voltage is applied to thecontrol pads 74 and 78, this causes the switch 60 to rotate in acounterclockwise position, as shown in FIG. 3C, causing the seesaw 62 toground the microstrip transmission line 64. In order to open thegrounding switch 60, a bias voltage is applied to the opposing controlpads 72, 76, which, in turn, causes the seesaw 62 to rotate in aclockwise direction, thus breaking the connection between the left sideof the seesaw 62 (FIG. 3A) and the microstrip transmission line 64. Thestops 80, 82 which are not grounded, prevent the seesaw fromre-contacting the microstrip transmission line 64 when a biasing voltageis applied to the opposite side control pads 72, 76.

The seesaw 62 may optionally be provided with one or more vent holes 84.The vent holes 84 facilitate the fabrication process as well as increasethe speed of operation of the switch 60. In particular, the vent holes84 facilitate removal of a sacrificial layer needed in fabrication. Inaddition, the vent holes 84 reduce the drag in the atmosphere, as wellas lower the mass, thus making the switch faster.

The embodiment illustrated in FIG. 4, generally identified with thereference numeral 86, is similar to the embodiment illustrate in FIG. 3Aand includes vent holes and a torsion bar except that the millimetergrounding switch 86 is disposed adjacent to a microstrip transmissionline 88. An RF Input is available on one end of the microstrip 88 and anRF Output is available on the other end. In this embodiment, the seesawrotates about an axis generally parallel to the longitudinal axis of themicrostrip 88. This embodiment allows for more room for the control padsand also allows for switching at lower voltages, for example, 10V, butotherwise is virtually the same as the millimeter wave switch 60described and illustrated in conjunction with FIG. 3A.

FIGS. 5-8 illustrate a broadband power switch configured as a singlepole double throw switch. Not only can the broadband power switchprovide operation at relatively high frequencies, but can also carryrelatively high RF Power. FIGS. 5-7 illustrate one embodiment of thebroadband power switch, while FIG. 8 illustrates an alternateembodiment.

Referring first to FIGS. 5-7, a broadband power switch, in accordancewith the present invention, is illustrated and generally designated withthe reference numeral 100. The embodiments illustrated in FIGS. 5-7relate to a single pole double throw switch formed from a single RFinput microstrip transmission line and two RF output microstriptransmission lines. Other configurations are also contemplated, such asa single pole single throw which includes a single input microstriptransmission line and a single output microstrip transmission line.

FIG. 5 illustrates the broadband power switch 100 with no biasingvoltage applied. The broadband power switch 100 includes a transversebeam 102, formed as an air bridge, formed generally traverse to aplurality of microstrip transmission lines 104, 106 and 108. Themicrostrip transmission line 104 forms an RF input line, while themicrostrip transmission lines 106 and 108 form RF output lines RF out 1and RF out 2, respectively. Unlike the ground switches illustrated inFIGS. 1-14, 1, 2, 3a and 4, the broadband power switch 100 selectivelyconnects an RF input transmission line 104 to one of two RF outputtransmission lines 106 and 108 forming a single pole double throwswitch.

The air bridge beam 102 is rigidly attached to a substrate (not shown)by way of end posts 110, 112 formed on each end from a thick metal layerdirectly on the substrate. One or both of the end posts 110, 112 isterminated by an RF grounding impedance 114 and thereby connected toground to allow charge flow so that the air bridge beam 102 can beattracted to the control pads.

As shown, two terminals 118, 120 are formed on the input microstriptransmission line 104 while a single terminal 116, 122 is formed on eachof the output RF transmission lines 106, 108, respectively.Additionally, the terminals 116, 118 are formed on one side of the beam102 while the terminals 120, 122 are formed on an opposing side of thebeam 102. The terminals 116, 118, 120, 122 are formed by an additionalmetalization layer on top of the microstrip transmission lines 104, 106and 108 to a height that enables contact with the beam 102 when it isdeflected either to the right or to the left to that shown in FIG. 5.

A plurality of control pads 124, 126, 128 and 130 are provided in orderto cause the beam to be deflected by electrostatic force. In particular,the control pads 124 and 128 are formed on one side of the beam 102,while the control pads 126 and 130 are formed on an opposing side of thebeam. As shown in FIG. 6, application of a biasing voltage, for example,+25V, to the control pads 126 and 130 causes the beam 102 to deflect tothe right, causing the beam to contact the terminals 120 and 122,thereby connecting RF input microstrip transmission line 104 to the RFoutput microstrip transmission line 108. Similarly, when a biasingvoltage, for example +25V, is applied to the control pads 124 and 128 asshown in FIG. 7, the beam 102 is reflected to the left, therebyconnecting the terminals 118 on the RF input transmission line 104 tothe terminal 116 on the RF output transmission 106.

An alternate embodiment of the broadband power switch is illustrated inFIG, 8. This embodiment is similar to the embodiment illustrated inFIGS. 5-7, except it includes two transverse beams 142 and 144. Thebroadband power switch 140 includes an input RF microstrip transmissionline 146 having a plurality of terminals 148, 150, 152 and 154. Twooutput RF transmission lines are provided. The first output RFtransmission line 156 is provided with a pair of terminals 160 and 162.Similarly, the second RF output transmission line 158 provides a pair ofoutput terminals 164 and 166.

The beams 142 and 144 are rigidly attached on each end to the substrate(not shown) by way of a plurality of end posts 168, 170, 172, 174. Inorder to cause deflection of the beams 142, 144, a plurality of controlpads 176, 178, 180, 182, 184, 186, 188 and 190 are provided. Applicationof the biasing voltage, for example +25V, to the various control pads176-190 176, 178, 180, 182, 184, 186, 188 and 190 causes deflection ofthe beams 142, 144 to connect various terminals 148, 150, 152 and 154 onthe RF input transmission line 146 to be connected to various terminals160, 162, 164 and 166 on the RF output transmission lines 156 and 158respectively. As shown, applying a biasing voltage to the control pads176, 180, 184 and 188 causes the beams 142 and 144 to deflect to theleft (FIG. 8) as shown. This deflection connects the RF input terminals148 and 152 to the terminals 160 and 162 on the RF output transmissionline 156. Similarly, applying a biasing voltage, for example, +25V, tothe control pads 178, 182 186 and 190 causes the beams to deflect to theright. This deflection connects the RF input terminals 150 and 154 tothe terminals 164 and 166 on the RF output transmission line 158.

Fabrication details for the planar air bridge grounding switch, seesawswitch and broadband power switch are illustrated in FIGS. 9A-9J. Inparticular, FIGS. 9A-9J illustrate an exemplary process of forming boththe air bridge and seesaw switches illustrated in FIGS. 1-8. FIGS.10A-10C illustrate a microstrip and identify the metalization layers ofthe seesaw switches illustrated in FIGS. 3A and 4.

Referring to FIGS. FIG. 9A-9J, the process is initiated by depositing athin metalization layer 200 on a wafer or substrate 202. Themetalization layer 200, identified as “METAL 1”, may be applied byconventional techniques. The metalization layer 200 may be deposited,for example to a thickness of 1000 angstroms.

As shown in FIG. 10C, the METAL 1 layer 200 may be used for forminginterconnections under the air bridge. For example, in the embodimentsof the air bridge shunt switch illustrated in FIGS. 1 and 2 and thebroadband power switch, illustrated in FIGS. 5-8, the thin metal layer200 is used to continue the transmission line under the bridge. Aphotoresist layer 204 is deposited over the METAL 1 layer 200, as shownin FIG. 9B. The photoresist layer 204 is spun onto the METAL 1 layer 200by conventional techniques. The photoresist layer 204 is then patternedand developed, as shown in FIG. 9C. The METAL 1 layer 200 is thenetched, and then the photoresist layer 204 is stripped, as shown in FIG.9D. A second photoresist layer 206 is applied as shown in FIG. 9E. Thesecond, sacrificial photoresist layer 206 is patterned and hard baked,as generally shown in FIG. 9F. This layer is hard baked to preventdevelopment in the next process steps. Next, as shown in FIG. 9G a thirdphotoresist layer 208 is spun on top of the substrate 202, METAL 1 layer200 and second photoresist layer 206, as generally shown in FIG. 9G. Thethird photoresist layer 208 is then patterned for the second metal layerMETAL 2, as generally shown in FIG. 9H. After the third photoresistlayer 208 is patterned, the second metal layer METAL 2, generallyidentified with the reference numeral 210 (FIG. 9I), is depositedthereupon by conventional techniques.

The second metal layer 210 is a relatively thick metal layer, forexample 20,000 angstroms and is used to form the air bridge and raisedcontacts that need to be at the same height as the bridge. The thickmetal layer 210 is also deposited on the transmission line away from thebridge and other electrodes in order to reduce resistance. Finally, asshown in FIG. 9J the second metalization layer 210 is “lifted off” andthe photoresist rinsed off to leave only portions of the metalcontacting METAL 1 or the substrate.

The process for making the seesaw switch, as illustrated in FIGS. 3A and4 is the same as illustrated in FIGS. 9A-9J. In particular, a thin metallayer, identified as METAL 1 which may be for example 2,000 angstroms isdeposited directly on the substrate. A relatively thick metal layer,identified as METAL 2, for example 20,000 angstroms, is elevated inplaces by use of the sacrificial photo METAL 2 resist layer 206. Thesecond metal layer 210 is elevated for the seesaw and the two torsionbars. The METAL 1 layer, identified with the reference numeral 200, isused by itself for interconnections under the seesaw so that it passesthrough without touching it. For example, in FIG. 3A, the thin metallayer METAL 1 is used to continue the transmission line under theseesaw. The thin layer, METAL 1 may also be used for the controlelectrodes. The thick metal layer, METAL 2 may also be deposited on thetransmission line away from the seesaw and other electrodes to reduceresistance.

FIGS. 10A-10C illustrate the placement of the metal layers, METAL 1 andMETAL 2 (FIGS. 10B and 10C) in the formation of seesaw type switchesillustrated in FIGS. 3A and 4. As shown, the see saw switch 62 (seeFIGS. 10b, 10c) includes a transmission line 64, a pair of control pads74 and 78, as shown in FIGS. 10a and 10b, end posts 65 and 66 andtorsion bars 68 and 70, as shown in FIGS. 10a and 10b.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. In particular, eachembodiment can be configured with coplanar lines rather than microstriplines. Thus, it is to be understood that, within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described above.

What is claimed and desired to be covered by a Letters Patent is as follows:
 1. A ground switch for use in millimeter wave applications, the grounding switch comprising: a transmission line defining an RF input and an RF output at opposing ends; an RF contact formed on said transmission line; one or more ground contacts adapted to be connected to ground, spaced apart from said transmission line and an air bridge, for grounding said transmission line; an air bridge beam formed adjacent said transmission line, said air bridge beam rigidly connected to a substrate at each end, said beam spaced away from said RF contact and said one or more ground contacts in an at rest position and configured to contact said RF contact and said one or more ground contacts in an actuated position; and one or more control pads disposed adjacent said transmission line, said one or more control pads adapted to receive biasing voltage to cause said beam to deflect to said actuated position.
 2. The ground switch as recited in claim 1, wherein said air bridge is generally transverse to said transmission line.
 3. The ground switch as recited in claim 2, wherein said RF ground contact is formed on said transmission line.
 4. The ground switch as recited in claim 3, wherein said air bridge beam is formed above said transmission line.
 5. The ground switch as recited in claim 4 A ground switch for use in millimeter wave applications, the ground switch comprising: a continuous transmission line defining an RF input and an RF output at opposing ends; an RF contact formed on said transmission line between the RF input and RF output; one or more ground contacts adapted to be connected to ground, spaced apart from said transmission line and an air bridge, for grounding said transmission line; an air bridge beam having a metal portion and formed adjacent said transmission line, said air bridge beam rigidly connected to a substrate at each end, said beam spaced away from said RF contact and said one or more ground contacts in an at rest position and configured so that the metal portion of the air bridge beam makes contact with said RF contact and said one or more ground contacts in an actuated position to form an RF conductive path to ground for the RF contact; and one or more control pads disposed adjacent said transmission line, said one or more control pads adapted to receive biasing voltage to cause said beam to deflect to said actuated position, wherein said one or more ground contacts are formed on the same side of said air bridge beam as said RF contact.
 6. The ground switch as recited in claim 1 5, wherein said air bridge beam is generally parallel to said transmission line.
 7. The ground switch as recited in claim 6, A ground switch for use in millimeter wave applications, the ground switch comprising: a continuous transmission line defining an RF input and an RF output at opposing ends; an RF contact formed on said transmission line between the RF input and RF output; one or more ground contacts adapted to be connected to ground, spaced apart from said transmission line and an air bridge, for grounding said transmission line; an air bridge beam having a metal portion and formed adjacent said transmission line, said air bridge beam rigidly connected to a substrate at each end, said beam spaced away from said RF contact and said one or more ground contacts in an at rest position and configured so that the metal portion of the air bridge beam makes contact with said RF contact and said one or more ground contacts in an actuated position to form an RF conductive path to ground for the RF contact; and one or more control pads disposed adjacent said transmission line, said one or more control pads adapted to receive biasing voltage to cause said beam to deflect to said actuated position, wherein said RF contact and said one or more ground contacts are formed on opposing sides of said air bridge beam.
 8. The ground switch as recited in claim 1, wherein at least two or more control pads are provided.
 9. The ground switch as recited in claim 8, A ground switch for use in millimeter wave applications, the ground switch comprising: a continuous transmission line defining an RF input and an RF output at opposing ends; an RF contact formed on said transmission line between the RF input and RF output; one or more ground contacts adapted to be connected to ground, spaced apart from said transmission line and an air bridge, for grounding said transmission line; an air bridge beam having a metal portion and formed adjacent said transmission line, said air bridge beam rigidly connected to a substrate at each end, said beam spaced away from said RF contact and said one or more ground contacts in an at rest position and configured so that the metal portion of the air bridge beam makes contact with said RF contact and said one or more ground contacts in an actuated position to form an RF conductive path to ground for the RF contact; and one or more control pads disposed adjacent said transmission line, said one or more control pads adapted to receive biasing voltage to cause said beam to deflect to said actuated position, wherein said control pads are formed on at least one side of said air bridged bridge beam.
 10. The ground switch as recited in claim 8, wherein said control pads are formed on both sides of said air bridged beam.
 11. The ground switch of claim 5 wherein the air bridge beam comprises a layer of movable metal and the RF contact extends outwardly from said transmission line.
 12. The ground switch of claim 7 wherein the air bridge beam comprises a layer of movable metal and the RF contact extends outwardly from said transmission line.
 13. The ground switch of claim 9 wherein the air bridge beam comprises a layer of movable metal and the RF contact extends outwardly from said transmission line.
 14. The ground switch of claim 5 wherein the air bridge beam deforms in the actuated position so that an intermediate portion of the air bridge beam bends towards the transmission line.
 15. The ground switch of claim 7 wherein the air bridge beam deforms in the actuated position so that an intermediate portion of the air bridge beam bends towards the transmission line.
 16. The ground switch of claim 9 wherein the air bridge beam deforms in the actuated position so that an intermediate portion of the air bridge beam bends towards the transmission line.
 17. The ground switch of claim 5 wherein the air bridge beam is disposed to move as a seesaw from the at rest position to the actuated position.
 18. The ground switch of claim 7 wherein the air bridge beam is disposed to move as a seesaw from the at rest position to the actuated position.
 19. The ground switch of claim 9 wherein the air bridge beam is disposed to move as a seesaw from the at rest position to the actuated position.
 20. The ground switch recited in claim 5, wherein said air bridge beam is generally transverse to said transmission line.
 21. The ground switch recited in claim 7, wherein said air bridge beam is generally transverse to said transmission line.
 22. The ground switch recited in claim 9, wherein said air bridge beam is generally transverse to said transmission line. 